diff --git a/.travis.yml b/.travis.yml
index 4038ea8..ad1894c 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -23,3 +23,5 @@ env:
     - PG_VERSION=10  CHECK_CODE=clang
     - PG_VERSION=10  CHECK_CODE=cppcheck
     - PG_VERSION=10  CHECK_CODE=false
+    - PG_VERSION=11  CHECK_CODE=false
+    - PG_VERSION=12  CHECK_CODE=false
diff --git a/Dockerfile.tmpl b/Dockerfile.tmpl
index 5e95748..eaf70c8 100644
--- a/Dockerfile.tmpl
+++ b/Dockerfile.tmpl
@@ -3,8 +3,9 @@ FROM postgres:${PG_VERSION}-alpine
 ENV LANG=C.UTF-8 PGDATA=/pg/data
 
 RUN if [ "${CHECK_CODE}" = "clang" ] ; then \
-	echo 'http://dl-3.alpinelinux.org/alpine/edge/main' > /etc/apk/repositories; \
-	apk --no-cache add clang-analyzer make musl-dev gcc; \
+	# echo 'http://dl-3.alpinelinux.org/alpine/edge/main' > /etc/apk/repositories; \
+	# Use alpine/v3.6/main instead of alpine/edge/main to fix version of clang to '8.*.*'
+	apk --no-cache add clang-analyzer make musl-dev gcc --repository http://dl-cdn.alpinelinux.org/alpine/v3.6/main; \
 	fi
 
 RUN if [ "${CHECK_CODE}" = "cppcheck" ] ; then \
@@ -12,14 +13,18 @@ RUN if [ "${CHECK_CODE}" = "cppcheck" ] ; then \
 	fi
 
 RUN if [ "${CHECK_CODE}" = "false" ] ; then \
-	echo 'http://dl-3.alpinelinux.org/alpine/edge/main' > /etc/apk/repositories; \
-	apk --no-cache add curl python3 gcc make musl-dev;\
+	# echo 'http://dl-3.alpinelinux.org/alpine/edge/main' > /etc/apk/repositories; \
+	# Use alpine/v3.6/main instead of alpine/edge/main to fix version of clang to '8.*.*'
+	# Install clang as well, since LLVM is enabled in PG_VERSION >= 11 by default
+	apk --no-cache add curl python3 gcc make musl-dev llvm clang clang-dev \
+		--repository http://dl-cdn.alpinelinux.org/alpine/v3.6/community \
+		--repository http://dl-cdn.alpinelinux.org/alpine/v3.6/main; \
 	fi
 
-RUN mkdir -p /pg/data && \
+RUN mkdir -p ${PGDATA} && \
 	mkdir /pg/src && \
 	chown postgres:postgres ${PGDATA} && \
-	chmod a+rwx /usr/local/lib/postgresql && \
+	chmod -R a+rwx /usr/local/lib/postgresql && \
 	chmod a+rwx /usr/local/share/postgresql/extension
 
 ADD . /pg/src
diff --git a/Makefile b/Makefile
index b6f70ea..8cd4d9a 100644
--- a/Makefile
+++ b/Makefile
@@ -26,3 +26,12 @@ endif
 
 $(EXTENSION)--$(EXTVERSION).sql: setup.sql
 	cat $^ > $@
+
+# Prepare the package for PGXN submission
+package: dist dist/$(EXTENSION)-$(EXTVERSION).zip
+
+dist:
+	mkdir -p dist
+
+dist/$(EXTENSION)-$(EXTVERSION).zip:
+	git archive --format zip --prefix=$(EXTENSION)-$(EXTVERSION)/ --output $@ master
diff --git a/run_tests.sh b/run_tests.sh
index 5e66bc9..f543fe1 100755
--- a/run_tests.sh
+++ b/run_tests.sh
@@ -48,7 +48,7 @@ make USE_PGXS=1 install
 status=$?
 if [ $status -ne 0 ]; then exit $status; fi
 
-# add pg_pathman to shared_preload_libraries and restart cluster 'test'
+# add pg_wait_sampling to shared_preload_libraries and restart cluster 'test'
 echo "shared_preload_libraries = 'pg_wait_sampling'" >> $PGDATA/postgresql.conf
 echo "port = 55435" >> $PGDATA/postgresql.conf
 pg_ctl start -l /tmp/postgres.log -w